1. Field of the Invention
The invention relates to crystal growth apparatus and particularly to a lid structure for a crystal growth crucible.
2. Description of the Prior Art
In the known Czochralski crystal growth method and apparatus, a heated crucible containing a melt often has an annular-shaped lid, also known as a “washer” for regulating thermal gradients within the crucible. Often the crucible and lid are constructed of a noble metal, such as iridium. A seed rod is inserted through the central aperture of the annular lid and oriented proximal the melt, so as to form a solid crystalline structure on the rod tip. As the seed rod is withdrawn from the crucible at a controlled rate an elongated crystal is formed. Structure and operation of crystal growth apparatus are generally known in the crystal fabrication art.
Crucible lids may be constructed by removing a generally annular planar-shaped ring from a metal blank sheet, analogous to forming a cookie from a sheet of dough. Fabrication waste remnants, typically iridium, left after removal of the lid from the sheet blank is valuable and is recycled by re-forming into a new sheet. As one skilled in the art can appreciate, removal of only an annular ring from a larger blank sheet likely creates a larger volume of remnant waste than the actual ring. Considerable effort is expended to form lid fabrication blanks, with a relatively low yield of finished lid product. Thus, a need exists in the art for a lid structure and fabrication method that reduces fabrication waste while increasing potential fabrication yield of lids.